Frequency divider



April 25, 1961 HAHNEL 2,981,899

FREQUENCY DIVIDER Filed Aug. 12, 1958 PC 0 l I 2 in f OUTPUT INVENTOR, ALWIN HAHNEL.

ATTORNEY.

U d W 1 The invention described herein may 'be manufactured and used by orforthe Governmentfor governmental purposeswithoutthe payment of any royalty thereon.

This invention relates to'frequency' dividers and particularly to frequency dividers of the locked-in oscillator type. n v a A general object of theinvention is to produce with a simple and'economical circuit arrangement by the process 'or frequency divisiona number of stable electric waves of frequencies'that are subharmonics of a given-frequency. "Anothergenerahobject is to improve frequency dividers having variable frequency division ratios. I Another obje'ct istoprovidewith a minimalamountfof circuitry 'crystalcontrol of frequencies below the'ftequency range for which quartz crystals can 'be' produce'd.

A'related object is to. adapt an oscillator of'the lockedin type so that itwill provide crystal-controlled low frequency outputs that are integrally related to the fundamental frequency'of aiquartz piezoelectriccrystal.

Another object 'is'to produce with a relatively simple circuit arrangement,containing inexpensive circuit elementsa plurality of "stable lowtrequency signals comprising a series of adjacent 'subharmonics of a given fundamental frequency, which circuit arrangement is such as'to' enable ready selectiontherefrom of any desired one of thegenerated subharmonicisignals without the use or i auxiliary frequency mixersiand selective circuits.

The frequency divider inaccordance with the invention for attainingthese objects isbasically an electrical oscil- "lationnetwork adapted to. "oscillate simultaneously at two 'widely different frequencies one of which is the crystalcjontrolled frequeney and'theother a selected'subharmonic 'of'th'at frequency. Inon e .'embodiment,' this frequency divider comprises two transistor amplifying triodes with' associated means for applying biasing. voltages to the transistor electrodes, a piezoelectric crystal for the control of the main frequency anda -LC resonant circuit tunable to th'e desi'red silbharmonic of the main frequency, intercon- 'riectedto form a regenerative closed loop network having "ofthat frequency. With proper selection of circuit con stems. in the'two. feedback sections of this regenerative network so that both signals f and f are simultaneously transmitted through the two non-linear transistor devices, these signals necessarily are harmonically related. The lower frequency section of this network locks itself to a subharmonic of the crystal frequency f determined by the tuning of the LC circuit, and thus provides a crystalcontrolled output at a frequency substantially lower than f and a wave of the desired subharmonic frequency may be taken off directly at any suitable point in the loop circuit.

The various objects and features of the invention will be better understood from the following complete description thereof when it is read in conjunction withthe drawing which shows a schematic circuit diagram of one embodiment of the frequency divider of the invention.

tent

crystal frequency f1- -case where theifreqeuncy determining LC circuit'RC is 2,981,899 i -Patented-Apr.25, 1961- 2 Referring to the drawin'g, the'frequency dividing circuitshown th'erein e'rnploys for its main 'elementstwo transistor amplifying devices T and T usually referred was transistor triodes, respectively having the usual, base electrodes b and 12 emitter'electrodes e and a and collector electrodes'c iiand c which transistor devices may be' -of the'P N P type as indicated conventionally by the direction of the arrows associated with the emitter electrodes e ande in the drawing. In order to make 10 the transist'Or t'riodes T and T operate as amplifiers,

their respectiveemitter electrodes e, and 2 which are connected directly to each other, are positively biased and theirrespec'tive collector electrodes c and 0 are negatively biased, withrespecfto their'base electrodes b and b 15 respectively, by the 'connection jof the emitter electrodes '3 and e to the p'ositive terminal ('B+) of an associated battery of {suitable voltage value through the common feedresistor'R and the connection of the base electrodes b and 12 and the collector electrodes 0 and c to the 20 negative terminal (B-) of the same battery through feed resistors R R and -R of suitably selected resistance values.

=A regenerative closed loop network including the two transistor t-ri'odesT 'and T is formed by the' following other connections. The emitter electrode e of the tran- {sistor triode T is connected directly to the emitter electrode e of the transistontriode T The collector electrode c of transistor triodeT is connected directly to the base electrode b 1of'the transistor'triode T Aseries connection isprovided from the collector electrode c of the transistor triodeT to'the base electrode [2 of transistor triode' T through the piezoelectric crystal 'PC adaptedfor-fs'eries'- resonance at a selected fundamentalfrequencyfgto'provide areg'enerative feedback path for the A separateserie's. connection is pro'vided' from' the emitter electrode 2 of the transistor triode T- to thebase' electrode b of transistor triode '13;

through the resistor R and aresonant circuit 'RC comp'risingthe i'nductor'L and the'capacitor C in series therewith, adapt'ed for"variable-tuning over a wide range of adjacent'subharmonicspf the fundamental frequency f -to prbvide a'"regenerative feedback path for any desired farmonicjgjwithin that range "to which the circuit RC is tuned. I Thewaveform obsei-ved at any point in this regenerative network when-the transistor triodes T and T are operatively ene'rgiz'ed, is periodic at the subharmonic frequericy f and, therefore, contains only spectrum com- ?ponents that 'are harmonically relatedto f one of which is identical to the frequency, f, of. the quartz crystal PC.

-Suitable selection 'ofjthe circuit constants of the two fe'edbackpaths so that both signals f and f are transmitted simultaneously through the two transistortriodes -T and T -results necessarily in the two signals being harmonically related. This applies :also inthe undesired .seri esfltuned such thattits' resonant frequency is halfway "between"the'frequencies 'of two adjacent subharmonics of the fundamental frequency 3. For this tuning condition of the circuit RC, the subharmonic frequency 1; established is such that one of its harmonics is identical to the second harmonic of h.

A stable wave of the subharmonic frequency f =f /n, where n is an integer=10, ll, 12, may be taken off directly from any convenient point in the regenerative oscillation network, for example, as indicated in the drawing, across the resistor R A crystal-controlled low frequency step oscillator substantially as shown in the drawing designed to provide frequency division in the ratio of one hundred to one, has been used in a transistorized version of a conventional radio receiver. As the frequency divider of the a a t, 2,981,899

3. invention does not require the frequency and selective circuits of conventional frequency dividers, it is especially useful in systems where miniaturization of circuit components or economy of circuitry is essential, such as quartz crystal-controlled low frequency standards.

The particular frequency divisioniratio, specified above for the frequency divider in accordance with the invention is given by way of example only. It is to be understood that by proper selection and adjustment of the circuit components other frequency'division ratios differing substantially from the ratio given may be obtained in accordance with the invention.

Various modifications of the circuit illustrated and described which are within the spirit and scope of the invention will occur to persons skilled in the art.

What is claimed is: Q

1. A frequency divider of the locked-in oscillator type comprising an amplifier including at least one pair of energized transistor amplifying triodes each having a base electrode and two output electrodes including an emitter and a collector, connected intandem with their emitters directly connected to each other, the collector of the output triode connected directly to the base electrode of the input triode, voltage supply means for positively biasing the emitter and negatively biasing the collector of each triode with respect to its base electrode, and two feedback paths each including individual frequency-determining means, respectively connected between a different output electrode of the output triode and the base electrode of the input triode of the amplifier and forming therewith a regenerative closed loop network oscillating under control of said frequency-determining means simultaneously at two widely separated frequencies one of which is a predetermined -main frequency f and the other of which is a selected subharmonic f of said main frequencyto cause signals of corresponding frequency to be fed back regeneratively over respective ones of the two paths, the relative circuit directly connected to the base electrode of the input stage, voltage supply means for positively biasing the emitter and negatively biasing the collector of each of said triode stages with respect to its base electrode, and two separate regenerative feedback paths connected between the emitter electrode and the collector electrode, respectively,

. of the output triode and the base electrode of the inconstants of said two feedback paths being selected such that the fedback signals are simultaneously transmitted through said triodes to maintain the harmonic relationship between them, and an output circuit connected to said network for taking off directly therefrom a stable "wave of the selected subharmonic frequency f 2. A frequency divider in'accordance with claim 1, in

which said two separate feedback paths respectively feeding back regeneratively around the loop through the frequency-determining means therein and said triodes, said predetermined main frequency and said selected sub "harmonic of said main frequency in such a phase relaselected subharmonic frequency.

3. A frequency dividing circuit for generating with crystal-controlled accuracy stable waves of different frequencies in a range too low for direct crystal control,

comprising an amplifier with two cascade-connected energized, transistor triode stages each having base, emitter and collector electrodes, with their emitters connected directly to each other, the collector of the output stage put triode of said amplifier and forming therewith a regenerative closed loop network, one of said paths including in series therewith a piezoelectric crystal resonant at a predetermined main frequency f,, for regeneratively feeding back a signal of that frequency and the second of said paths including in series therewith a series inductancecapacitance resonant circuit selectively tunable to any desired subharmonic f in a plurality of adjacent subharmonics of said main frequency f,, for regeneratively feeding back a signal of the selected subharmonic f the circuit constants of the two feedback paths being selected such as to insure that both fedback signals 1, and f will be transmitted simultaneously through the two transistor triode stages thereby maintaining a harmonic relationship between these signals, and output means for taking off a generated signal of the selected subharmonic frequency f directly from said regenerative network.

4. A frequency divider comprising two transistor amplifying triodes each having an emitter, a collector and a base electrode, voltage supply means for positively bias ing the emitter and negatively biasing the collector of each triode with respect to its base electrode, said triodes being interconnected in tandem to form a regenerative closed loop network in which the emitters of the two triodes are directly connected to each other, the collector of one triode is connected directly to the base electrode of the other triode, the collector of said other triode is connected to the base electrode of said one triode through a series piezoelectric crystal resonant at a predetermined main frequency f to provide one regenerative feedback path for signals of that frequency and the emittter of said other triode is connected to the base electrode of said one triode through a resistor and a series inductance-capacitance resonant circuit selectively tunable to any desired subharmonic in a plurality of adjacent subharmonics of said main frequency f,, in series to provide a second regenerative feedback path for signals of the selected subharmonic frequency f;,, the circuit constants of the two feedback paths being selected to insure that both signals .of frequency f, and f are'transmitted simultaneously through the two tandem-connected transistor triodes and .thus are maintained in harmonic relationship, and an output circuit connected across the resistor in said second feedback path for taking off therefrom the generated sig- .nal of the selected subharmonic frequency f References Cited in the file of this patent UNITED STATES PATENTS Hammett July 28, 

